How Much Calorie Restriction Is Enough to Slow Brain Aging?

Caloric restriction (CR), which is reduced calorie intake without essential nutrient deficiency (i.e. a state of undernutrition without malnutrition) has been associated with improved cognition, a slowing of overall brainaging, and protection against neurodegenerative diseases - at least in animal models. Currently, however, very little is known about the benefits of CR on the human brain, especially if the CR diet is initiated later in life. Most of the recent animal studies were initiated when the animals were rather young in order to detect the largest possible benefits.

Although the exact mechanisms underlying the beneficial effects of CR are not known, a calorically restricted diet is known to impart beneficial effects on health and extend lifespan in a large variety of species ranging from worms to monkeys. Evidence suggests that a reduction in inflammatory processes underlies at least part of CRs beneficial effects along with decreases in oxidative stress. I've discussed the role of these factors in previous blogs.

Interestingly, low body weight associated with starvation in both intentional (e.g. anorexia nervosa, bulimia, and hunger strike) and unintentional cases (war) is linked with smaller brain volume and does not show significant beneficial effects.

In a recently published study (Bendlin et al., Neurobiology of Aging, 2012), a large group of monkeys, ranging in age from middle-aged adults to the quite elderly, were fed only 70% of their free-feeding diet for about 15 yrs. Essentially, for someone eating a 2000 calorie per day diet, this would be about 600 fewer calories per day; for comparison, 600 calories would be about one cup of roasted almonds, or a 100 gram bar of dark chocolate, or a typical Cold Stone Creamery dessert (with the M & M's!).

As a result of eating just 30% fewer calories, the brains of the monkeys on the CR diet aged significantly more slowly. Although several brains regions showed benefits, those brains regions that evolved most recently, such as the frontal lobes, and therefore tend to be more vulnerable to the consequences of aging, showed the greatest beneficial response to CR. Monkeys on the CR diet have previously been shown to develop far fewer age-related diseases, have virtually no indication of diabetes, almost no age-related muscle atrophy, and live much longer (Colman et al., Science, 2009).

Take notice of the crucial fact that these monkeys did not exercise the weight off, they simply consumed fewer calories. Unless you plan on becoming a long distance runner, or something similar, exercising is never going to be as beneficial to your brain and body as restricting the number of calories you consume!

The comparisons you used in the fourth paragraph were poorly chosen. A person who eats only 2000 calories a day is unlikely to eat a whole cup of almonds or a 100 grams of chocolate in one day. You make it sound as though that person would only be giving up luxuries to follow a calorie restricted diet.

For a person who eats 2000 calories a day spread out over three meals and two very small snacks, that person would actually be giving up the equivalent of an entire meal.

The positive effects of vitamin B, C, D and E with harmful effects of trans fats (which are common in processed foods, including cakes, biscuits and fried foods) about brain shrinkage typical of Alzheimer's emphasized in this work.

Interesting. I wonder if the effect would be the same if we created the 600 calorie deficit by both a food intake reduction (of lesser proportions) AND pyshical activity. I don't want to be a thin, flabby unfit person, but rather a thin, physically fit person. And, I really like those endorphins that kick in with a good cardio. I would be concerned that the strictly reduced calorie scenario would leave a person without enough energy to go for a walk or jog on a gorgeous afternoon, for instance. Is the slowing of cognitive decline a worthy trade off to being otherwise physically fit?

You have absolutely nailed the basic dilemma. We know that taking in calories ages us, however, does that doom us to total inactivity? Thus, we must all find the compromise position, i.e. just enough exercise to keep us as fit as we wish but not so much that we age too quickly. No one wants to be so weak that they cannot enjoy life, particularly the long life and better health provided by CR.

You have absolutely nailed the basic dilemma. We know that taking in calories ages us, however, does that doom us to total inactivity? Thus, we must all find the compromise position, i.e. just enough exercise to keep us as fit as we wish but not so much that we age too quickly. No one wants to be so weak that they cannot enjoy life, particularly the long life and better health provided by CR.

The most important factors for brain health are regular mental and physical exercise and natural nutrition according to the current studies. Dietary restrictions excepts for trans fats are not among the first recommendations.